Among conventional power supply systems for vehicle of this type, a power supply system for vehicle has been proposed which, upon deceleration of a vehicle, aggressively performs regeneration of braking energy by setting the voltage of generated power of an electric generator which is driven by an engine and feeds power to a battery, to be higher than the voltage upon non-deceleration, and meanwhile, upon non-deceleration of the vehicle, reduces load on the engine to improve fuel efficiency by setting the voltage of generated power of the electric generator to be lower than the voltage upon deceleration (for example, see Patent Document 1 shown below).